Lasker's Trap can be very powerful weapon for Black in Albin Counter gambit variation. The unusual though very powerful feature of Lasker Trap is underpromotion on seventh move. It is a good idea to use this opening in quick games since it is not very often played and your opponent most likely would be unprepared for it. Let's take a closer look:

1. d4 d5 2. c4 e5 3. dxe5 d4 4. e3 Bb4+ 5. Bd2 dxe3 6. Bxb4 exf2+7. Ke2 fxg1N+ 8. Ke1 Qh4+ 9. Kd2 Nc6 10. Bc3 Bg4 -+

White plays 1.d4, Black replies 1...d5 2. c4.

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White hopes to face "standardized" d4 opening lines such as 2...e6 or 2...c6 (Slav/Semi Slav) but, here the surprise comes: 2...e5. Black attacks the center directly offering a counter gambit for White's Queen's Gambit, called Albin Counter gambit. 3. dxe5 d4 4.e3?
This move is not very bad for White, but that's exactly what Black wants, playing Counter gambit earlier (a lot safer is 4.Nf3!). Now 4...Bb4+ 5.Bd2 dxe3! Black sacrifices a bishop and if White take it they are in big trouble. Here the best bet for White is to accept double pawns, playing 6.fxe3 and after 6...Qh4+ 7.g3 Qe4
Black is somewhat better and White needs a precise defense to remain in game.

Here we see what happens if White takes the bishop 6.Bxb4? exf2+. White cannot take that pawn with a king now, since it looses a queen. So, 7.Ke2 and Black plays 7...fxg1=N!!+. Here the under promotion concept comes into play. In some positions promoting a pawn into less valuable piece (here the knight) wins a game. White cannot take the knight with the rook: 8.Rxg1 since 8... Bg4+ looses a queen. The best move for White here is 8.Ke1Qh4+ 9.Kd2 (9. g3? looses a rook after 9...Qe4+ ) 9...Nc6 10.Bc3 Bg4 followed by 11...O-O-O and White's best move is to resign :)